Motion-picture film



May 15, 1923. 1,455,428

c. J. COBERLY MOTION PICTURE FILM Filed Feb. 8, 1917 WI E/VTOR:

HTTORNEYZS'.

Patented May 15, 1923.

UNITED STATES CLARENCE J. COBERLY, OF LOS ANGELES, CALIFORNIA.

MOTION-PICTURE FILM.

Application filed February 8, 1917. Serial No. 147,505.

To all whom it may concern:

Be it known that I, CLARENCE J. COBERLY, a citizen of the United States,residing at Los Angeles, in the county of Los Angeles and State ofCalifornia haveinvented a new and useful Motion-Picture Film, of whichthe following is a specification.

My invention relates to the art of producing motion pictures. In thatart a great deal of expense is caused by the necessity of retakingscenes due to the appearance of static markings on the film afterdevelopment. These static markings are due to disruptive discharges ofstatic electricity which collect on the film due to friction orinduction during the process of manufacture ofv the film or in thecamera. Celluloid, of which the majority of motion picture film 1s made,is naturally an insulator and is capable of generating electric chargesby friction and ofv isolating such charges until they come into theneighborhood of a grounded body, at which time the charges aredischarged. The property of isolating charges,

2 which depends on the high insulating char acteri'stics of the film, ismodified by surrounding atmospheric conditions. The greater the degreeof humidity in the air the less likelihood there is of the chargesaccumulating, as leakage through the air and leakage over the surface ofthe film is greatly facilitated by the presence of moisture.

The princi al object of my invention is to prevent t e formation ofcharges of static electricity on the film. This I accomplish by greatlyincreasing the electrical conductivity of the film either by placing aconducting coating on the film itself or by adding to the film amaterial which will renderit an electrical conductor. I prefer to add acoating, as in this way the chemical and ph sical characteristics of thefilm proper are unaltered. There are several methods of addingsuchelectrical conduct- 4 inc coatings, but many of them are open to theobjection that they affect the transparency of the film or otherwiseinterfere with its ordinary functions, or make it hard to handle. Iprefer to add as a coating a body of hygroscopic material which willtake up sufiicient moisture even at very low'humidities to form a thinlayer of water over the surface of the film, which, due to the presenceofmetallic salts therein, will immedidiately serve to conduct away anyelectrical charges which ma tend to collect. I further find that lithlumchlorideis an excellent substanceto use for this purpose.

Further objects and advantages will be set forth more in detailhereinafter.

The drawing shows a film embodying my invention.

In the film shown, 11 is a celluloid support or body having a lightsensitive coating formed of a body of emulsion 12 fixed to one sidethereof. The celluloid being a poor conductor of electricity, it isossible to accumulate electric charges t ereon, these charges beingeither frictionally produced or produced by induction from other chargedbodies.

Broadly considered, my invention consists in rendering the film a betterconductor, or in providing the ordinary celluloid film with a conductivebacking, this backing being applied to the opposite side of thecelluloid from the emulsion.

In practice, I prefer to provide such a backing rather than to t toembody my invention in the celluloi itself. I have found that if theback of the film, that is to say the side opposite the emulsion, has ahygroscopic salt deposited thereon this salt willv collect and retainmoisture and the film of water, with the salt in solution, will form aconducting surface through which electric charges can be readilydissipated, thus preventing the accumulation of electric charges.

I coat the back of the film with a thin layer, of a hygroscopic saltwhich may be carried in a. solvent which is afterwards evaporated.Apparatus for coating film being old in the art, I have not illustratedsame. In practice, I prefer to use lithium chloride as the salt, andalcohol as the solvent and I have found that one ounce of lithiumchloride is sufficient to treat 5000 linear feet of ordinary motionpicture film which is one and three-eighths inches wide.

It is possible to work the invention with salts that are not thoroughlyhygroscopic. These salts must, however, have the property of collectingand retaining some vapor carried in the air thus forming an electricallyconducting solution or electrolyte.

This vapor may be alcohol vapor, or the vapor of some other substancewhich is liquid at ordinary temperatures and pressures, and which iseither a conductor itself or has the propertyof forming anelectricallyconducting solution or electrolyte.

It is of course necessary in such cases to saturate the air intheneighborhood of the film while it is being exposed or otherwise handledwith alcohol or similar vapor. This can be conveniently done by placingan open vessel containing alcohol or the like in the camera.

In the practical operation of my invention the lithium chloride, orother salt, is deposited on the film after the emulsion has been fixedthereon and before the film has been exposed. Under ordinary conditionsof humidity, there is suflicient moisture in the air to keep the back ofthe film moist, so that it will at all times be a good 0011- ductor ofelectricity. In some cases it is desirable to place asupply of water oralcohol in the camera or film container for the purpose of sup lyingvapor. I find that by keeping the Elm moist it retains its originalcharacteristics and shape much better than where free evaporation cantake place.

It will thus be seen that my invention consists broadly in theconception of rendering the film a conductor, so that the electro-staticcharges will be carried away.

It consists further in the conception-of coating an ordina celluloidfilm with such a conducting bac ing. This, of course, could beaccomplished by other means than the hygroscopic material outlinedabove.

The invention consists further in applying to the back of a standardfilm a body of hygroscopic material, or material which has an afiinityfor hygroscopic vapors, for the purpose of collecting and retaining afilm of water on the back of the motion picture film.

My invention further consists in the use of lithium chloride for theabove purposes.

While my, invention is entitled motion picture film, it is evident thatI have invented a new and useful improvement in the motion picture artwhich may well be called a method of preventing static.

All of-these embodiments of my invention are new and useful, andmy'conception thereof is embodied in the following claims.

I am aware that other inventors have proposed to use photographic filmswhich contain. a metallic layer. These films are, of course, opaque andcannot be used in the place of the standard transparent motion picturefilm now in common use. Such films, however, contain an electricallyconducting layer and it is not my intention to claim broadly any filmcontaining an electrically conducting layer.

My invention differs from films containing 'a metallic layer in that itutilizes electrolytic conduction to carry off the electr1c charge ratherthan metallic electrical con duction which might occur in the case of afilm having a metal layer.

By electrolytic conduction I mean such electrical conduction as occursthrough solutions either in water or other substances. I have alreadyindicated that alcohol or other substances may be used in the place ofwater and a skilled chemist could substitute many other substances whichwould form conducting electrolytes with lithium chloride or itsequivalents.

In electrolytic conduction the substance in solution is ionized and actsas a carrier of electricity, positive ions appearing at one end of theconducting path and negative ions appearing at the other. Suchelectrolytic conduction is, of course, accompanied by a decomposition ofthe electrolyte, the amount of such decomposition being proportional tothe amount of energy transmitted. In the practiceof my invention, theamount of energy is small and the amount of material decomposed isnegligible, and therefore unobj ectionable.

While the alcohols and other substances,

as already pointed out, may be used in the place of water to form theelectrolyte it is obvious that water is the most convenient substance touse for this purpose.

Also while I have specified lithium chloride as a preferred material itwill be obvious to a skilled chemist that many other substances arecapable of going into solution, becoming ionized, and supportingelectrolytic conduction.

I claim as my invention:

1. A motion picture film comprising a transparent support; a layer ofsensitized emulsion; and a layer of lithium chloride, sa1d layer oflithium chloride being on the opposite side of said support from thelayer of emulsion.

2. A motion picture film having a layer of material which is hygroscopic1n atmospheres of seventy percent relative humidity or below.

3. A motion picture film' having a light sensitive coating; a supportfor said coating, sa1d coating and support being so constituted, if usedalone, that static markings may be produced in said coating, and a layerof material, on said film, which is sufliciently hygroscopic to preventsaid markings from occurring in an atmosphere of seventy percenthumidity or below.

4. A motion picture film having a sup port; a light sensitive coatingcarried by said support, said support and said coating being of such anature, if used alone, that static markings may be produced in saidcoating, under ordinary conditions of use of said motion picture film;and a layer on said film containing hygroscopic material, said saidfilm, the static markings which might layer being sufficientlyelectrically conductotherwise be produced by said use. ing to preventsaidmarkings. In testimony whereof, I have hereunto set 1 5. A motionpicture film having a layer my hand at Los Angeles, California, this 5containing a solution, said solution belng 29th day of January, 1917.

sufliciently electrically conducting to prevent, under the usualconditions of use of CLARENCE J. COBERLY.

